Method and apparatus for dispensing a viscous material on a substrate

ABSTRACT

A dispenser, configured to dispense material on a substrate, includes a dispensing unit having a housing with a chamber, a piston disposed in the chamber and axially movable within the chamber, and a nozzle coupled to the housing. The nozzle has an orifice co-axial with the chamber of the housing. The dispenser further includes an actuator coupled to the dispensing unit and configured to drive the up- and down movement of the piston, and a compliant assembly coupled to the actuator and the piston. The compliant assembly is configured to permit limited relative travel between the actuator and the piston. A method of dispensing is further disclosed.

RELATED APPLICATIONS

This application is a divisional of pending U.S. patent application Ser.No. 13/801,421, filed Mar. 13, 2013, entitled METHOD AND APPARATUS FORDISPENSING A VISCOUS MATERIAL ON A SUBSTRATE, which is incorporatedherein by reference in its entirety.

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

The invention relates generally to methods and apparatus for dispensinga viscous material on a substrate, such as a printed circuit board.

2. Discussion of Related Art

There are several types of prior art dispensing systems or dispensersused for dispensing metered amounts of liquid or paste for a variety ofapplications. One such application is the assembly of integrated circuitchips and other electronic components onto circuit board substrates. Inthis application, automated dispensing systems are used for dispensingdots of liquid epoxy or solder paste, or some other related material,onto circuit boards. Automated dispensing systems are also used fordispensing lines of underfill materials and encapsulants, whichmechanically secure components to the circuit board. Underfill materialsand encapsulants are used to improve the mechanical and environmentalcharacteristics of the assembly.

Another application is to dispense very small amounts or dots onto acircuit board. In one system capable of dispensing dots of material, adispenser unit utilizes a rotating auger having a helical groove toforce material out of a nozzle and onto a circuit board. One such systemis disclosed in U.S. Pat. No. 5,819,983, entitled LIQUID DISPENSINGSYSTEM WITH SEALING AUGERING SCREW AND METHOD FOR DISPENSING, which isowned by Speedline Technologies, Inc. of Franklin, Mass., a subsidiaryof the assignee of the present disclosure.

In an operation employing an auger-type dispenser, the dispenser unit islowered towards the surface of the circuit board prior to dispensing adot or a line of material onto the circuit board and raised afterdispensing the dot or line of material. Using this type of dispenser,small, precise quantities of material may be placed with great accuracy.The time required to lower and raise the dispenser unit in a directionnormal to the circuit board, typically known as a z-axis movement, cancontribute to the time required to perform dispensing operations.Specifically, with auger-type dispensers, prior to dispensing the dot orline of material, the dispenser unit is lowered so that the materialtouches or “wets” the circuit board. The process of wetting contributesto additional time to perform the dispensing operation.

It is also known in the field of automated dispensers to launch dots ofviscous material toward the circuit board. In such a system, a minute,discrete quantity of viscous material is ejected from a nozzle withsufficient inertia to enable the material to separate from the nozzleprior to contacting the circuit board. As discussed above, with theauger-type application or other prior, traditional dispensing systems,it is necessary to wet the circuit board with the dot of material toenable the material to adhere to the circuit board such that when thedispenser is pulled away the dot of material will release from thenozzle. When ejecting, the dots may be deposited on the substratewithout wetting as a pattern of discrete dots, or alternatively the dotsmay be placed sufficiently close to each other to cause them to coalesceinto more or less a continuous pattern. An example of such a system isdisclosed in U.S. Pat. No. 7,980,197, entitled METHOD AND APPARATUS FORDISPENSING A VISCOUS MATERIAL ON A SUBSTRATE, which is owned by IllinoisTool Works Inc. of Glenview, Ill., the assignee of the presentdisclosure.

SUMMARY OF THE DISCLOSURE

One aspect of the disclosure is directed to a dispenser configured todispense material on a substrate. In one embodiment, the dispensercomprises a dispensing unit including a housing having a chamber, apiston disposed in the chamber and axially movable within the chamber,and a nozzle coupled to the housing. The nozzle has an orifice co-axialwith the chamber of the housing. The dispenser further comprises anactuator coupled to the dispensing unit and configured to drive the up-and down movement of the piston, and a compliant assembly coupled to theactuator and the piston. The compliant assembly is configured to permitlimited relative travel between the actuator and the piston.

Embodiments of the dispenser further may include a sensor to sense aposition of the actuator. The dispenser further may include a sensor tosense a position of the piston. The dispenser further may include acontroller for controlling the actuator. The controller may beconfigured to perform a feed-forward adaptive routine. The controllerfurther may be configured to utilize sensor data from the sensor and thefeed-forward adaptive routine to control motion of the actuator toachieve a desired actuator motion profile. The compliant assemblyfurther may be configured to bias a length of the compliant assembly toan extended position. The compliant assembly may include a housingcoupled to the actuator and a plunger disposed within the housing at alower end of the housing, with the plunger being biased to an extendedposition. The compliant assembly further may include a spring disposedbetween the housing and the plunger, with the spring being configured tobias the plunger to the extended position. The plunger of the compliantassembly may be configured to apply a downward bias on the piston, and,during a downward stroke of the piston, the plunger engages the pistonand the spring is compressed within the housing. In one embodiment, theactuator may be a piezoelectric actuator assembly. In anotherembodiment, the actuator may be a voice coil motor. In one embodiment,the piston stops when a tip of the piston engages a seat, and thecompliant assembly permits further travel of the actuator subsequent tothe engagement of the piston against the seat. In another embodiment,the piston stops when a feature of the piston engages a stop, and thecompliant assembly permits further travel of the actuator subsequent tothe engagement of the piston against the stop. The compliant assemblymay have a stiffness of compliance, with the compliant assembly beingconfigured to vary a stiffness of compliance as a function of relativemotion between the actuator and the piston.

Another aspect of the disclosure is directed to a method of operating adispenser to dispense material on a substrate. In one embodiment, thedispenser comprises a dispensing unit including a housing having achamber, a piston disposed in the chamber and axially movable within thechamber, and a nozzle coupled to the housing, the nozzle having anorifice co-axial with the chamber of the housing, and an actuatorcoupled to the dispensing unit and configured to drive the up- and downmovement of the piston. The method comprises permitting limited relativetravel between the actuator and the piston.

Embodiments of the method further include biasing a length of thecompliant assembly to an extended position. The method further mayinclude varying a stiffness of compliance as a function of relativemotion between the actuator and the piston. The method further mayinclude sensing a position of the actuator and/or sensing a position ofthe piston. The method further may include controlling the actuator byproviding a feed-forward adaptive routine to utilize sensor data fromthe sensor and the feed-forward adaptive routine to control motion ofthe actuator to achieve a desired actuator motion profile.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the disclosure, reference is made to thefigures which are incorporated herein by reference and in which:

FIG. 1 is a schematic view of a dispenser of an embodiment of thedisclosure;

FIG. 2 is a perspective view of a portion of a dispenser of anembodiment of the disclosure;

FIG. 3 is a cross-sectional view of a dispensing unit of the dispenserof an embodiment of the disclosure;

FIG. 4 is an enlarged cross-sectional view of a nozzle of the dispensingunit shown in FIG. 3;

FIG. 5 is a cross-sectional view of a dispensing unit of the dispenserof another embodiment of the disclosure;

FIG. 6 is an enlarged cross-sectional view of a nozzle of the dispensingunit shown in FIG. 5;

FIG. 7 is a cross sectional view of the dispensing unit shown in FIG. 3having a heated assembly mounted on a housing of the dispensing unit;

FIG. 8A is a cross-sectional view of a portion of an actuator assemblyconfigured to operate the dispensing unit shown in FIGS. 3 and 4;

FIG. 8B is a cross-sectional view of a portion of an actuator assemblyconfigured to operate the dispensing unit shown in FIGS. 5 and 6;

FIG. 9 is a perspective view of a piezoelectric actuator assemblyoperating the dispensing unit shown in FIG. 3;

FIG. 10 is a cross-sectional view with cross-hatching removed to moreclearly illustrate the piezoelectric actuator assembly shown in FIG. 9;

FIG. 11 is another cross-sectional view with cross-hatching removed tomore clearly illustrate the piezoelectric actuator assembly shown inFIG. 9; and

FIG. 12 is a perspective view of a voice coil motor actuator assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of illustration only, and not to limit the generality,the disclosure will now be described in detail with reference to theaccompanying figures. This disclosure is not limited in its applicationto the details of construction and the arrangement of components setforth in the following description or illustrated in the drawings. Thedisclosure is capable of other embodiments and of being practiced orbeing carried out in various ways. Also the phraseology and terminologyused herein is for the purpose of description and should not be regardedas limiting. The use of “including,” “comprising,” “having,”“containing,” “involving,” and variations thereof herein, is meant toencompass the items listed thereafter and equivalents thereof as well asadditional items.

FIG. 1 schematically illustrates a dispenser, generally indicated at 10,according to one embodiment of the present disclosure. The dispenser 10is used to dispense a viscous material (e.g., an adhesive, encapsulant,epoxy, solder paste, underfill material, etc.) or a semi-viscousmaterial (e.g., soldering flux, etc.) onto an electronic substrate 12,such as a printed circuit board or semiconductor wafer. The dispenser 10may alternatively be used in other applications, such as for applyingautomotive gasketing material or in certain medical applications. Itshould be understood that references to viscous or semi-viscousmaterials, as used herein, are exemplary and intended to benon-limiting. The dispenser 10 includes first and second dispensingunits or heads, generally indicated at 14 and 16, respectively, and acontroller 18 to control the operation of the dispenser. Although twodispensing units are shown, it should be understood that one or moredispensing units may be provided.

The dispenser 10 may also include a frame 20 having a base or support 22for supporting the substrate 12, a dispensing unit gantry 24 movablycoupled to the frame 20 for supporting and moving the dispensing units14, 16, and a weight measurement device or weigh scale 26 for weighingdispensed quantities of the viscous material, for example, as part of acalibration procedure, and providing weight data to the controller 18. Aconveyor system (not shown) or other transfer mechanism, such as awalking beam may be used in the dispenser 10 to control loading andunloading of substrates to and from the dispenser. The gantry 24 can bemoved using motors under the control of the controller 18 to positionthe dispensing units 14, 16 at predetermined locations over thesubstrate. The dispenser 10 may include a display unit 28 connected tothe controller 18 for displaying various information to an operator.There may be an optional second controller for controlling thedispensing units.

Prior to performing a dispensing operation, as described above, thesubstrate, e.g., printed circuit board, must be aligned or otherwise inregistration with a dispenser of the dispensing system. The dispenserfurther includes a vision system 30, which is coupled to a vision systemgantry 32 movably coupled to the frame 20 for supporting and moving thevision system. Although shown separately from the dispensing unit gantry24, the vision system gantry 32 may utilize the same gantry system asthe dispensing units 14, 16. As described, the vision system 30 isemployed to verify the location of landmarks, known as fiducials orother features and components, on the substrate. Once located, thecontroller can be programmed to manipulate the movement of one or bothof the dispensing units 14, 16 to dispense material on the electronicsubstrate.

Systems and methods of the present disclosure are directed to theconstruction of the dispensing units 14, 16. The description systems andmethods provided herein reference exemplary electronic substrates (e.g.,printed circuit boards), which are supported on the support 22 of thedispenser 10. In one embodiment, the dispense operation is controlled bythe controller 18, which may include a computer system configured tocontrol material dispensers. In another embodiment, the controller 18may be manipulated by an operator.

Referring to FIG. 2, an exemplary material deposition system, generallyindicated at 200, may be configured from a XYFLEXPRO® dispenser platformoffered by Speedline Technologies, Inc. of Franklin, Mass., a subsidiaryof the assignee of the present disclosure. In one embodiment, thematerial deposition system 200 includes a frame 202 that supportscomponents of the material deposition system, including but not limitedto a controller, such as controller 18, which is located in a cabinet ofthe material deposition system. As shown, the material deposition system200 further includes two deposition or dispensing units, generallyindicated at 204 and 206, for depositing low viscous materials (e.g.,less than 50 centipoise), semi-viscous materials (e.g., 50-100centipoise), viscous materials (e.g., 100-1000 centipoise), and/or highviscous materials (e.g., greater than 1000 centipoise). The depositionunits 204, 206 may be movable along orthogonal axes by a gantry system,generally indicated at 208, under the control of the controller 18 toallow dispensing of the material on the circuit board, such as substrate12, which, as mentioned above, may sometimes be referred to as anelectronic substrate or a circuit board. A cover (not shown) may beprovided but is not shown so as to reveal the internal components of thematerial deposition system 200, including the deposition units 204, 206and the gantry system 208. Although two deposition units 204, 206 areshown and described, any number of deposition units may be provided andfall within the scope of the present disclosure.

Circuit boards, such as substrates 12, which are fed into the materialdeposition system 200, typically have a pattern of pads or other surfaceareas onto which material will be deposited. The material depositionsystem 200 also includes a conveyor system 210 that is accessiblethrough an opening 212 provided along each side of the materialdeposition system to transport the circuit board in an x-axis directionto a depositing position in the material deposition system. Whendirected by the controller of the material deposition system 200, theconveyor system 210 supplies circuit boards to a dispense location underthe deposition units 204, 206. Once arriving at the position under thedeposition units 204, 206, the circuit board is in place for amanufacturing operation, e.g., a deposition operation.

The material deposition system 200 further includes a vision inspectionsystem, such as the vision system 30 shown in FIG. 1, that is configuredto align the circuit board and to and inspect the material deposited onthe circuit board. In one embodiment, the vision inspection system issecured to one of the deposition units 204, 206 or to the gantry system208. To successfully deposit material on the circuit board, the circuitboard and the deposition units 204, 206 are aligned, via the controller18. Alignment is accomplished by moving the deposition units 204, 206and/or the circuit board based on readings from the vision inspectionsystem. When the deposition units 204, 206 and the circuit board arealigned correctly, the deposition units are manipulated to perform adeposition operation. After the deposition operation, optionalinspection of the circuit board by means of the vision inspection systemmay be performed to ensure that the proper amount of material has beendeposited and that the material has been deposited at the properlocations on the circuit board. The vision inspection system can usefiducials, chips, board apertures, chip edges, or other recognizablepatterns on the circuit board to determine proper alignment. Afterinspection of the circuit board, the controller controls movement of thecircuit board to the next location using the conveyor system, where anext operation in the board assembly process may be performed, forexample electrical components may be placed on the circuit board or thematerials deposited on the board may be cured.

In some embodiments, the material deposition system 200 may operate asfollows. The circuit board may be loaded into the material depositionsystem 200 in a depositing position using the conveyor system. Thecircuit board is aligned with the deposition units 204, 206 by using thevision inspection system. The deposition units 204, 206 may then beinitiated by the controller 18 to perform a deposit operation in whichmaterial is deposited at precise locations on the circuit board. Oncethe deposition units 204, 206 have performed a depositing operation, thecircuit board may be transported by the conveyor system from thematerial deposition system 200 so that a second, subsequent circuitboard may be loaded into the material deposition system. The dispositionunits 204, 206 may be constructed to be quickly removed and replacedwith other units.

Referring to FIG. 3, a dispensing unit, generally indicated at 300, ofan embodiment of the present disclosure is shown and will be describedbelow. As shown the dispensing unit 300 includes a housing 302 and anozzle assembly, generally indicated at 304, which is releasably securedto the housing. Specifically, the dispenser housing 302, which iscoupled to an actuator along axis A, is configured to define an elongatechamber 306, which is designed to receive viscous material fordispensing. A seal nut 308 and suitable seals 310 secure an upperportion of a piston guide or chamber structure 312 within the chamber306 of the housing 302. A lower portion of the piston guide 312 issecured by the nozzle assembly 304, which includes a nozzle nut 314 anda valve seat 316 upon which the lower portion of the piston guide 312rests. The cylindrical chamber 306 defines a dispensing cavity that isin fluid communication with a material feed tube 318, which is adaptedto receive material from a material supply assembly. As shown, thematerial feed tube 318 introduces viscous material within the chamber306 at the upper portion of the piston guide 312 through an inlet 320.As will be described in greater detail below, the viscous material isdelivered to the chamber 306 to the small dispensing cavity underpressure. The dispensing unit 300 further includes a reciprocatingpiston 322 that is partially disposed within the seal nut 308 and thepiston guide 312. The piston 322 has an upper end that is biased by ayoke in a downward manner by a spring and a plunger, which is actuatedby the actuator, and a lower end configured to engage the valve seat316. The piston 322 is configured to be received and slidably movedwithin the chamber 306 along axis A.

Referring to FIG. 4, the lower portion of the dispensing unit 300 isillustrated. As shown, the nozzle nut 314 is threadably secured to alower portion of the housing 302 and configured to secure the valve seat316 between the nozzle nut and the lower end of the piston guide 312.The valve seat 316 includes a generally cylindrical member having aconical surface 400 and a small-diameter bore 402, e.g., 0.005 inches indiameter, formed therein. In one embodiment, the valve seat 316 may befabricated from a hard material, such as synthetic sapphire. Thearrangement is such that viscous material is ejected from thesmall-diameter bore 402 onto a substrate, e.g., circuit board 12, whenthe piston 322 engages the valve seat 316. In a particular embodiment,the nozzle assembly 304 may be provided as a complete assembly to theend user of the dispenser 300 to aid in cleaning of the nozzle assembly.Specifically, a used nozzle assembly 304 may be completely removed fromthe housing 302 of the dispensing unit 300 by unscrewing the needle nut314 and replaced with a new (clean) nozzle assembly.

In operation, the reciprocating piston 322 is moveable between an upperposition and a lower position within the piston guide 312 providedwithin the chamber 306 of the housing 302. The dispensing medium, e.g.,solder paste, is introduced under pressure into the chamber 306 throughthe inlet 320 and the dispensing material flows through slits 404 formedin the piston guide 312 to an open space above the valve seat 316. Inthe lower position, the piston 322 is seated against the valve seat 316and in the upper position, the piston is raised out of the valve seat ofthe nozzle assembly. As described below, the actuator assembly includesone of a piezoelectric actuator or a voice coil motor, which is coupledto the piston 322, and operation of the actuator assembly (via a flexureassembly) causes the movement of the piston between the upper and lowerpositions. When the piston 322 moves to its lowered position against thevalve seat 316, a small drop of material is dispensed through the smalldiameter bore 402 formed in the valve seat.

As discussed, the dispensing unit 300 provides pressurized air to thesource of dispensing material to introduce the material into the housingof the dispensing unit by the material feed tube 318. The particularpressure provided may be selected based on the material being used,volume of material being dispensed, and mode of operation of thedispensing unit 300. During operation of the dispenser, a user, throughthe user interface for the dispensing platform, defines dispensing areason a circuit board. The dispensing unit 300 may be used to dispense dotsand lines of material. When the dispensing unit 300 is used to dispenselines of material formed through multiple dispensing cycles of thedispenser and is used to dispense material at selected locations on acircuit board or other substrate using an individual dispensing cycle.For lines of material, a user defines the start and stop positions of aline, and the dispensing platform is able to move the dispensing unit300 to place material along the line. Once all dispensing areas on acircuit board are defined and the dispensing parameters set using adispensing unit control panel, the dispenser is able to receive circuitboards for processing. After moving a circuit board to a dispensinglocation, the dispenser controls the gantry system 208 to position thedispensing unit over a dispensing location. In another embodiment, thecircuit board may be moved under a stationary dispensing unit.Dispensing for a particular board will continue until material has beendispensed at all locations on the board. The board is then unloaded fromthe system and a new board can be loaded into the system.

Referring to FIG. 5, a dispensing unit, generally indicated at 500, ofanother embodiment of the present disclosure is shown and will bedescribed below. As shown the dispensing unit 500 includes a housing 502and a nozzle assembly, generally indicated at 504, which is releasablysecured to the housing. Specifically, the dispenser housing 502, whichis coupled to an actuator along axis B, is configured to define anelongate chamber 506 configured to receive viscous material fordispensing. A seal nut 508 and suitable seals 510 secure an upperportion of a piston guide 512 within the chamber 506 of the housing 502.A lower portion of the piston guide 512 is secured by the nozzleassembly 504, which includes a nozzle nut 514 and a nozzle 516configured to be held by the nozzle nut. The chamber 506 defines a smalldispensing cavity that is in fluid communication with a material feedtube 518, which is adapted to receive material from a material supplyassembly. As shown, the material feed tube 518 introduces viscousmaterial within the chamber 506 at the upper portion of the piston guide512 through an inlet 520. As will be described in greater detail below,the viscous material is delivered to the chamber 506 under pressure. Thedispensing unit 500 further includes a piston 522 that is disposedwithin the seal nut 508 and the piston guide 512. The piston 522 has anupper end secured to an actuator by a flexure assembly, and a lower endconfigured to move into and out of a small orifice 524 formed in thelower portion of the piston guide 512. The piston 522 is configured tobe received and slidably moved within the cylindrical chamber along axisB. A stop 526 is provided within a recess formed in the seal nut 508.The stop 526, which may be formed from compliant material, engages ahead of the piston 522 to stop the downward movement of the piston 522during a dispense operation.

Referring to FIG. 6, the lower portion of the dispensing unit 500 isillustrated. As shown, the lower end of the piston 522 is configured tomove through the small orifice 524 so that it ends up in a positionabove the nozzle 516. The nozzle 516 includes a generally cylindricalmember having a conical surface 600 and a small-diameter bore 602, e.g.,0.005 inches in diameter, formed therein. In one embodiment, the nozzle516 may be fabricated from a hard material, such as synthetic sapphire.The arrangement is such that viscous material is ejected from thesmall-diameter bore 602 onto a substrate, e.g., circuit board 12, whenthe piston 522 displaces the material provided within the space abovethe nozzle 516 and below the end portion of the piston guide 512. In aparticular embodiment, the nozzle assembly 504 may be provided as acomplete assembly to the end user of the dispenser to aid in cleaning ofthe nozzle assembly. Specifically, a used nozzle assembly may becompletely removed from the dispensing unit 500 by unscrewing the needlenut and replaced with a new (clean) nozzle assembly.

Referring to FIG. 7, an optional nozzle heater assembly, generallyindicated at 700, may be used with the dispensing unit, e.g., dispensingunit 300, and a temperature of the nozzle heater assembly may be setusing a user interface that is coupled to the controller 18. It shouldbe noted that the optional nozzle heater assembly 700 may be used fordispensing unit 500 and fall within the scope of the present disclosure.The nozzle heater assembly 700 is controlled by the system to maintainthe heater at a set temperature. The nozzle heater assembly 700 isconstructed to be attached to the lower portion of the housing 302 ofthe dispensing unit, e.g., the nozzle nut 314 as shown in FIG. 7, toprovide heat to the material above the valve seat 316. In oneembodiment, the nozzle heater assembly 700 includes a body 702, whichincludes a cartridge heater, a temperature sensor, and mountinghardware. The body 702 has a lower opening through which the lowerportion of the dispensing unit 300, i.e., the nozzle assembly 304,extends. Clamps may be provided to secure the nozzle heater assembly 700to the dispensing unit 300 by compressing the body 702 housing againstthe nozzle nut 314 of the nozzle assembly 304. The cartridge heater andthe temperature sensor may be coupled to the system controller, whichmaintains the temperature in the vicinity of the temperature sensor to aset value.

Referring to FIG. 8A, in one embodiment, the upper end of the piston 322is secured to a compliant flexure assembly, sometimes referred to as acompliant assembly, generally indicated at 800, which is configured tosecure the piston to the actuator assembly to provide reciprocatingaxial movement of the piston. As shown, the upper end of the piston 322includes a head portion 802. The compliant flexure assembly 800 includesa generally cylindrical flexure housing 804, which may be secured to alever arm of a piezoelectric actuator assembly by a screw 806. Inanother embodiment, the compliant flexure assembly 800 may be secured toa voice coil motor actuator assembly. The flexure housing 804 includes areduced thickness portion or flexure element 808, which enables theflexure assembly 800 to accommodate the arcuate motion of the lever armof the piezoelectric actuator assembly as it drives the reciprocalmotion of the flexure assembly and the piston 322.

The flexure assembly 800 further includes a spring housing 810 disposedwithin the flexure housing 804, a plunger 812 disposed within the springhousing at a lower end of the spring housing and axially movable withinthe spring housing, and a spring 814 disposed between the spring housingand the plunger. The plunger 812 includes yoke fingers 816 configured tocapture the head portion 802 of the piston 322. The compliant flexureassembly 800 further includes a rod 818 disposed within the flexurehousing 804 and the spring housing 810, the rod having a lower end thatis secured to the plunger 812. The arrangement is such that the plunger812 of the flexure assembly 800 is configured to apply a downward biason the head portion 802 of the piston 322.

Specifically, during operation of the dispensing unit 300, the actuatorassembly drives the up-and-down movement of the flexure assembly 800 andthe piston 322. During a downward stroke in which the piston 322 engagesthe valve seat 316, the actuator assembly and flexure assembly 800 has atendency to continue driving downwardly even though the piston hasabruptly stopped moving. During this motion, the plunger 812 engages thehead portion 802 of the piston 322 and the spring 814 is compressedwithin the spring housing 810 as the flexure housing 804 continues itsdownward movement. When the piston 322 is in a sealed position withinthe valve seat 316, the spring 814 is configured to bias the plunger 812downwardly to firmly seat the piston within the valve seat, therebyclosing the dispensing unit 300.

The flexure assembly 800 may further include a second flexure element820 disposed about the flexure housing 804 at a lower end of the flexurehousing. In one embodiment, the second flexure element 820 may embody aspider flexure that enables two degrees of movement, e.g., vertical andpitch, which further assists in accommodating the arcuate motion of thelever arm of the piezoelectric actuator assembly as it drives theup-and-down movement of the piston 322.

Referring to FIG. 8B, in another embodiment, the upper end of the piston522 is secured to a compliant flexure assembly, sometimes referred to asa compliant assembly, generally indicated at 850, which is configured tosecure the piston to an actuator assembly, such as the piezoelectricactuator assembly, to provide reciprocating axial movement of thepiston. As with flexure assembly 800, the flexure assembly 850 may besecured to a voice coil motor actuator assembly. As shown, the upper endof the piston 522 includes two spaced-apart head portions 852, 854. Theflexure assembly 850 includes a yoke 856 that is constructed to securethe upper head portion 852 of the piston 522 within the space betweenthe two head portions 852, 854 of the piston. The flexure assembly 850further includes a generally cylindrical flexure housing 858, which isoperated by the actuator assembly. For the piezoelectric actuatorassembly, the flexure housing 858 may include a reduced thicknessportion or flexure element (not shown in FIG. 8B), which enables theflexure assembly 850 to accommodate the arcuate motion of the lever armas it drives the reciprocal motion of the flexure assembly and thepiston 522.

The flexure assembly 850 further includes a spring housing 860 disposedwithin the flexure housing 858, a plunger 862 disposed within the springhousing at a lower end of the spring housing and axially movable withinthe spring housing, and a spring 864 disposed between the spring housingand the plunger. The arrangement is such that a lower end of a rod 866is secured to the plunger 862 to provide the axial movement of thepiston 522 within the spring housing 858 as described above. A stop 526may be provided to stop the movement of the piston 522 by engaging thelower head portion 854 of the piston. The arrangement is such that theplunger 862 of the flexure assembly 850 is configured to apply adownward bias on the head portion 852 of the piston 522. Specifically,during operation of the dispensing unit 500, the actuator assemblydrives the up-and-down movement of the flexure assembly 850 and thepiston 522. During a downward stroke in which the head portion 854 ofthe piston 522 engages the stop 526, the actuator assembly and flexureassembly 850 has a tendency to continue driving downwardly even thoughthe piston has abruptly stopped moving. During this motion, the plunger862 engages the head portion 852 of the piston 522 and the spring 864 iscompressed within the spring housing 860 as the flexure housing 858continues its downward movement.

FIG. 9 illustrates a piezoelectric actuator assembly, generallyindicated at 900, operating a dispensing unit 300, 500 of embodiments ofthe present disclosure. As shown, the piezoelectric actuator assembly900 includes a housing 902 configured to secure the dispensing unit 300,500 thereto. The housing 902 of the piezoelectric actuator assembly 900is suitably secured to the gantry 208 to move the dispensing unit duringa dispensing operation.

Referring to FIGS. 10 and 11, the piezoelectric actuator assembly 900 isshown with dispensing unit 300. It should be understood that thepiezoelectric actuator assembly 900 may be used with dispensing unit 500and fall within the scope of the present disclosure. The housing 902 ofthe piezoelectric actuator assembly 900 is configured to support thecomponents of the piezoelectric actuator assembly. As shown, thepiezoelectric actuator assembly is secured to the flexure assembly 800to effect the rapid up-and-down movement of the piston 322.Specifically, the piezoelectric actuator assembly 900 includes a leverarm 1100 having an end portion 1102 configured to be secured to theupper end of the flexure housing 804 of the flexure assembly 800. Thepiezoelectric assembly further includes a piezoelectric stack interfaceblock 1104, a mounting block 1106, and a hinge 1107 disposed between thelever arm 1100 and the interface block 1104 and the mounting block. Thehinge 1107 includes two pivot points 1108, 1110 that enable the leverarm 1100 to rock or pivot with respect to the up-and-down movement ofthe interface block 1104. The interface block 1104 is moved in anup-and-down direction by a piezoelectric stack 1112, which is positionedabove the interface block. In one embodiment, the result is that thepiezoelectric stack 1112 is capable of moving the interface block adistance of 65 microns (0.065 millimeters). The movement of theinterface block 1104 via the lever arm 1100 causes the axial movement ofthe flexure assembly to be 650 microns (0.65 millimeters). Thepiezoelectric stack can operate at a speed up to 1,000 Hertz. Theflexure assembly 800 is configured to address any unwanted lateralmovement of the piston 322 as the piston reciprocates in an up-and-downmovement. Thus, the piezoelectric actuator assembly 900 is capable oftranslating the movement of the piezoelectric stack 1112 to produceup-and-down movement of the flexure assembly 800, which in turn producesthe up-and-down movement of the piston 322.

The piezoelectric actuator assembly 900 further includes a sensorassembly generally indicated at 1114 to provide a closed-loop detectionof the movement of the piezoelectric actuator assembly. Specifically,the sensor assembly 1114 includes a lever arm sensor 1116 configured todetect a target provided on the lever arm 1100 to determine the movementof the lever arm 1100, and a rod sensor 1118 configured to detect atarget provided on an upper end of the rod to determine the movement ofthe rod 818. The lever arm sensor 1116 is secured to the housing 902 andis positioned a predetermined distance from the target provided on thelever arm 1100. This predetermined distance or gap is detected by thelever arm sensor 1116 to determine the amount of movement of the leverarm 1100 during operation. Similarly, the rod sensor 1118 is secured tothe housing 902 and is positioned a predetermined distance from thetarget on the rod 818. This predetermined distance or gap is detected bythe rod sensor 1118 to determine the amount of movement of the rod 818during operation. With the rod sensor 1118, the upper end of the rod 818has a sensor target 1120 to provide an object for the rod sensor todetect.

The sensor assembly 1114 may be used as part of a control system toprovide feed-forward control of the reciprocating motion of the piston.An adaptive routine may be provided that can vary drive signals used todrive the actuator assembly to ensure a desired motion profile isachieved, even as operating parameters, such as viscosity, vary. Forexample, viscosity of the material can change with time and temperature.This change in viscosity may cause a load on the actuator assembly tochange, and thus alter an actual motion achieved. By sensing this changein motion profile, subsequent drive signals can be adjusted as requiredto maintain a desired motion profile. Since these operating parameterchanges tend to drift slowly with time and temperature, the feed-forwardadaptive routine can track these variations in real time. This isdifferent in nature from a feed-back control system, in which the drivesignal is varied in real time at the full bandwidth of the system. Theadaptation in the feed-forward control system only needs to adapt atrates faster than the variations for which it is intended to compensate.An overwhelming advantage of feed-forward control systems is that unlikefeed-back control systems, they can be designed to be unconditionallystable.

The upper end of the rod 818 is further connected to a plunger assemblyhaving two ball plungers 1122, 1124 and a release lever 1126 connectedto the ball plungers. The two ball plungers 1122, 1124 force the releaselever 1126 out of the way (down) during regular operation. With therelease lever 1126 out of the way, the dispensing unit can operatefreely with no restrictions of the range of motion. When the dispensingunit is released, power is dropped from the piezoelectric stack 1112 thelever arm 1100 moves to a known location. To release the piston, thecompliance spring 814 of the flexure assembly 800 is compressed to freeup the head 802 of the piston 322. This is achieved by lifting up on therelease lever 1126, which compresses the ball plungers 1122, 1124. Thereare two sets of screws (not designated) provided on the release lever1126. The two sets of screws lift up on the bottom of a target, which inturn lifts on the rod 818, which lifts on the plunger 812, which finallycompresses the spring 814 and frees up the piston 322.

In another embodiment, a voice coil motor actuator assembly may beprovided to operate the dispensing unit, e.g., dispensing unit 300 or500. The voice coil motor actuator assembly is well known in the art andmay be suitably coupled to the dispensing unit to drive the operation ofthe piston 322 or 522. For example, FIG. 12 illustrates a voice coilmotor actuator assembly, generally indicated at 1200, operating adispensing unit, e.g., dispensing unit 300 or 500. As shown, the voicecoil motor actuator assembly 1200 includes a housing 1202 configured tosecure the dispensing unit thereto at location 1204. The housing 1202 ofthe voice coil motor actuator assembly 1200 is suitably secured to thegantry 208 to move the dispensing unit during a dispensing operation. Inone embodiment, the voice coil motor actuator assembly may include athree coil/3 pole/2 magnet motor.

In operation, the dispensing unit 300 or 500 is positioned at a nominalclearance height above the substrate, e.g., circuit board 12. Thisclearance height is maintained at a relatively consistent elevationabove the circuit board throughout the dispense operation, althoughvariations in the height of the circuit board, or irregularities in theflatness of the top surface of the circuit board, may cause theclearance height to vary without adversely impacting the dispensing ofviscous material. Specifically, the dispenser unit does not need to liftthe nozzle away from the circuit board in the z-axis direction at theend of each dispense operation. However, to accommodate variations inthe height of the circuit board and irregularities in the flatness ofthe circuit board (or to even avoid obstacles), the dispenser may beconfigured to achieve z-axis movement. In certain embodiments, a laserdetection system may be used to determine a height of the dispenser.

Thus, it should be observed that a feature of the present disclosure isthe axial compliance of the compliant flexure assembly 800. Thiscompliance permits the piston 322 to stop abruptly when it contacts thevalve seat 316, or when the lower head portion 854 of the piston 522contacts the stop 526, while permitting additional motion of the flexureassembly 800 past this point of contact. The compliant flexure assembly800 permits limited relative travel between the actuator assembly (viathe flexure housing 804) and the piston 322 or 522. This decoupling ofmotion reduces the shock loads to the actuator assembly, increases therapidity with which the piston may be decelerated, and in some modes ofoperation, permits a more energy efficient operation by converting thekinetic energy of the flexure assembly to potential energy in thecompressed compliance spring, and subsequently recovering this potentialenergy as kinetic energy of the actuator as the spring works toaccelerate the actuator in the opposite direct. As shown and described,the compliant flexure assembly 800 is further configured to extend alength of the assembly, i.e., the plunger 812 or 862, to an extendedposition. The compliant flexure assembly 800 has a stiffness ofcompliance. The compliant flexure assembly 800 is configured to vary astiffness of compliance as a function of relative motion between theactuator and the piston.

In a certain embodiment, the dispenser may be based on an existingplatform, such as platform dispensing systems that are offered under thebrand names FX-D and XyflexPro+, and operates using dispensing software,such as software that is offered under the brand name Benchmark, whichare offered by Speedline Technologies, Inc. of Franklin, Mass., asubsidiary of the assignee of the disclosure.

A method of operating a dispenser to dispense a volume of viscousmaterial on a substrate is further disclosed. The dispensing unit may bedispensing unit 300 or 500, which is coupled to actuator assembly 900 or1200. In one embodiment, the method includes connecting a piezoelectricactuator assembly 900 to the piston. The piezoelectric actuator assembly900 is configured to drive the up- and down movement of the piston. Themethod further includes activating a piezoelectric stack 1112 to drivethe up-and-down movement of a flexure assembly 800 and a piston 322. Ina certain embodiment, the piezoelectric stack 1112 operates at a speedbetween zero and 1,000 Hertz. The method may further include limitingunwanted lateral movement of the piston 322 as the piston reciprocatesin an up-and-down movement by the flexure assembly 800. The method mayfurther include sensing the movement of the actuator assembly to provideclosed loop operation of the dispenser. The method further may includecontrolling the operation of the piezoelectric actuator assembly with acontroller 18. The controller 18 is configured to move the piston 322from a pre-dispense position in which viscous material is introducedinto the chamber 306 to a dispense position in which the pistondispenses viscous material from the chamber and through the valve seat316.

Alternate embodiments of the present disclosure may include variousmechanisms to accomplish the compliant advantages of the compliantflexure assembly 800. For example, one embodiment may incorporatehydraulic components to vary the stiffness of compliance as a functionof the relative velocity between the housing 804 and the plunger 812. Anexample of this type of mechanism is a hydraulic valve lifter as used inmodern internal combustion engines.

Having thus described at least one embodiment of the disclosure, variousalternations, modifications and improvements will readily occur to thoseskilled in the art. Such alterations, modifications and improvements areintended to be within the scope and spirit of the disclosure.Accordingly, the foregoing description is by way of example only and isnot intended to be limiting. The limit is defined only in the followingclaims and equivalents thereto.

What is claimed is:
 1. A method of operating a dispenser to dispense material on a substrate, the dispenser comprising a dispensing unit including a housing having a chamber, a piston disposed in the chamber and axially movable within the chamber, and a nozzle coupled to the housing, the nozzle having an orifice co-axial with the chamber of the housing, an actuator coupled to the dispensing unit and configured to drive the up- and down movement of the piston, and a compliant assembly separate from the actuator, the method comprising: permitting limited relative travel between the actuator and the piston wherein the compliant assembly is secured to the piston and to the actuator assembly to provide reciprocating axial movement of the piston in response to the actuator, the compliant assembly including a flexure housing secured to the lever arm of the actuator and coupled to the piston to permit limited relative travel between the actuator and the piston during operation.
 2. The method of claim 1, further comprising biasing a length of the compliant assembly to an extended position.
 3. The method of claim 1, wherein the actuator is a piezoelectric actuator assembly.
 4. The method of claim 1, wherein the actuator is a voice coil motor.
 5. The method of claim 1, wherein the piston stops when a tip of the piston engages a seat, the method further comprising permitting further travel of the actuator subsequent to the engagement of the piston against the seat.
 6. The method of claim 1, wherein the piston stops when a feature of the piston engages a stop, the method further comprising permitting further travel of the actuator subsequent to the engagement of the piston against the stop.
 7. The method of claim 1, further comprising varying a stiffness of compliance as a function of relative motion between the actuator and the piston.
 8. The method of claim 1, further comprising sensing a position of the actuator.
 9. The method of claim 8, further comprising sensing a position of the piston.
 10. The method of claim 8, further comprising controlling the actuator by providing a feed-forward adaptive routine to utilize sensor data from the sensor and the feed-forward adaptive routine to control motion of the actuator to achieve a desired actuator motion profile.
 11. The method of claim 1, further comprising sensing a position of the piston.
 12. The method of claim 11, further comprising controlling the actuator by providing a feed-forward adaptive routine to utilize sensor data from the sensor and the feed-forward adaptive routine to control motion of the actuator to achieve a desired actuator motion profile. 